Intercommunicating telephone system



Dec. 29, 1936.

4M. BEAUMONT INTERCOMMUNICATING TELEPHONE SYSTEM Filed Sept. 26, 1935 /N VENTO/e WMBEAUMo/vr TTORNEV Patented Ejec. 29, 1936 attesti INTERO OlVllVIU NICATIN G TELEPHNE SYSTEM William M. Beaumont,

Summit, N. J., assignor to Bell Telephone Laboratories, incorporated, New York, N. Y., a corporation of New York Application September 26, i935, Serial No. Li-2,l92

Il Claims.

'This invention relates to telephone systems and more particularly to intercommunicating systems whereby any two stations of a particular group may signal and conversev with each other and wherein one or more trunk circuits extend to a telephone central office to which any station in the group may connect by operating a proper key, thus obtaining central ofce service.

All object of the invention is to permit a trunk circuit to be held by an answering station while disconnected from the trunk for the purpose of communicating with another station of the group and to insure removal of the holding condition when any station of the group is again connected to the trunk.

Another object is to preserve a balanced condition across the trunk at all times and to prevent inductive disturbances such as cross-talk in the system from aiecting conversation over the trunk.

A feature of the invention whereby the rst object is obtained resides in a holding bridge comprising a multi-wound relay, one winding of whichis connected in series with the answering station telephone across the trunk at the will of the subscriber whereupon the relay operates and locks itself operated across the trunk over its contacts and a second one of its windings, in series with a resistance, under control of a relay serially connected in the trunk which series relay operates to cause the first relay to release when any station of the system again connects to the trunk.

Another feature, whereby the second object is obtained, resides in a third or compensating winding l on the relay which opposes the first winding with respect to inductive disturbances, and is connected to a conductor which parallels and is exposed to the same inductive disturbance as the conductor to which the rst winding is connected.

The invention will be understood from the following description when read in connection with the accompanying drawings which illustrate an intercommunicating telephone system consisting of a plurality of subscribers stations, both master and controlled, a trunk circuit associated with these stations and extending to a central cice or to a private branch exchange; and a trunk holding circuit which embodies the features of this invention.

Two master stations are shown, one being rep-- resented by the subscribers set IUI and associated'key-'set |02 while the other is represented yby subscribers station |03 together with the as- (Ci. MEF-412) sociated key-set indicated by block |84. Two controlled stations are shown, one being represented by subscribers set E and the second by subscribers set |06. The master station key-set |82 is provided with three keys: a talking key I for establishing talking connections between the subscribers set mi and the trunk |00; a'holding key i l2 for holding an incoming trunk call while communicating with other stations of the group, if desired; and an intercommunicatingkey ||3 for establishing talking connections between station iii and other stations of the group. Block iill represents a key-set identical with key-set m2 and associated with the master station subscribers set W3. Keys i131 and |518, which are associated with the controlled station subscribers sets |85 and |36, respectively, provide means for connecting sets lol and m8 to trunk |00 for communication.

On an incoming call, ringing current applied to trunk Hit at the central ofce or private branch exchange, not shown, causes ringer ||0 in series with condenser |89 to sound. Assuming that the subscriber at master station set IUI answers the call, the talking key of the associated key-set it? is depressed and the-receiver at subscribersset lill is removed from the switchhook. The talking key is of a locking type well-known in the art and upon its operation completes a circuit from the trunk |00 to the subscribers set. This circuit is traceable from the upper or tip conductor of trunk |60, right front contact of key lll, right back contact of key H2, subscribers set lill, left back contact of key M2, leftfront contact of key Hl, winding of relay H5, to the lower or ring conductor of trunk Idil. Relay l I5 operates in this circuit from battery and ground supplied over the trunk from the central oiice or the private branch exchange but performs no useful function at this time. Conversation between the. calling subscriber (not shown) and the answering subscriber at station ll may now ensue.

Should it be desired to transfer the call to some other station of the intercommunicating group, this is accomplished as follows: The talking key iii of key-set m2 is, at this time, in its operated position and locked as previously set forth. The subscriber at station lill now momentarily depresses holding key l l2 of key-set |62. This holding key is of the non-locking type and the construction of key-set lilZ is such that the depression of holding key H2 releases the associated locking type talking key l' or intercommunicat ing key H3 if either of these latter keysare in their operated and locked position. Since talking key was previously operated and locked,V

the depression of holding key H2, therefore, causes talking key I I to release and restoreto its normal position. The release of key H| opens the circuit between subscribers set |0| Yand the conductors of trunk |00 through the winding of relay H5 thereby causing relay H5 to release. The trunk circuit, however, is not opened .at this time as an alternate bridge circuit across the trunk was substituted by the operationY of key H2 which can be traced from the upper conductor of trunk |00, outer right contacts of key H2, through the subscribers set |0|, outer left contacts of key I I 2, conductor |22 and lowerrwinding of relay H4 to the lower conductor of trunk |00 at .a point between theV relay H5 and the central oiice or private branch exchange, whereupon relay I 4 operates and locks in a circuit from the upper conductor of the trunk, through the upper winding of the relay, resistance H5, front Contact of `the relay, tothe lower'trunk conductor.

The release ofthe holding key I I2 by the subscriber at station |0| opens the operating circuit through the klower winding of relay H4 which relay, however, remains locked through its upper winding Vas set forth above and thereby, due to the bridge placed across, trunk |00 by the upper winding of relay I4 in series with resistance I6, rcauses the connection on` the trunk to be held. The restoration of holdingkey H2 to its normal position also` opens the circuit between subscribers set 0| and trunk |00. Y

The subscriber'at station |0| now depresses the intercommunicating key H3 which locks in its operated position and connects station |0| to thelocal intercommunicating line conductors Il and H8 over the back contacts of keys H2 and |H and the front contacts of key H3. Potential for local transmission between stations of the intercommunicating` group is supplied vto conductors H1 and H8 through the windings of retardation coils H9 and |20. Having connected set ||||v to conductors H1 and H8 by the operationof intercommunicat-ing key H3 of the associated key-set |02, the subscriber at station |0| nowQsignals the particular controlled kstation or other master-station at which it is desired that the incoming call be taken up. This signaling Asystem (not, shown) is independent of the talking conductors H'l and H8 and may consist of anytype of system, either audible or visual, an audiblev system using buzzers on a code signaling basis usually being employed. As thissignaling system forms nopart ofthe present invention, no further reference to it will be made.

Assumingl that the subscriber at station |0| signalsthe subscriber at the controlled station |06 and this latter subscriber, in response to the signal, removes his receiver from the switch-hook, he is thereuponin communication with thesubscriber at station |0| over intercommunicating line conductors H'| and H8. Upon being advised that an incoming call is waiting, the subscriber at station |06 operates the associatedlocking type key |08. The operation of key |08 transfers subscribers station |06 from its normal connection withthe intercommunicating line conductors H1 and H8 to the tip and ring conductors of trunk |00 in series with trunk relay H5 whichv relay. again operates on the current supplied over .the trunk from the central oice orrprivate branch exchange. The operation of relay |5.shortcircuits the upper winding of hold- 'ing' relay H4 which thereupon releases. The

- release of relay H4 removes the holding bridge consisting of the upper winding of relay I4 in series withresistance H6 from across trunk |00. The calling subscriber and the subscriber at station |00 are now in direct communication.

At the conclusion of conversation, the ksubscriber at station |06 replaces his receiver on the switch-hook and restores key |08 toits normal position. Trunk relay H5 thereupon releases and opens the short-circuit around the upper wind- .ing of relay I4 thereby restoring the trunk holding circuit to normal.

Should it be desired that the incoming call, originally answered by the subscriber at master station |0| be taken up by some other subscriber than the one at controlled station |06 as set forth above, the subscriber at station |0| communicates with the proper station and the call is taken up and the trunkholding circuit restored in the manner identical with that hereinbefore described. If the call is taken up at station |05, trunk relay H5 operates in series with the subscribers set atV station|05 when the receiver at` that station is removed from the switch-hook and the associated key |01 is operated. is taken up at station |03, trunk relay I5 operates in series with the subscribers set at station |03 when the receiver at that station is removed kfrom the switch-hook and the talking key of the associated key-set |04, similar to key HI of key- If the call set |02, is operated. In either case, the operation f of relay H5 causes the release of relay H4 and 1 restores the trunk holding circuit as already described.

The keys associated with each of the masterand controlled subscribers stations o f the intercommunicating group are usually interconnected-;

with each other, with the central oillce or private branch exchange trunk |00 and with the associated trunk holding circuit by means of a multi, conductor cable |2|. Since the lower or operatingwinding of relay H4 is permanentlyconnected to the lower conductor of trunk I 00 and the other curring in any of the various cable conductors adjacentv to the multiple conductor |22.

To prevent the interference of inductive disturbances from affecting yconversation over the trunk, the holding relay H4 is provided with` a third or compensating winding in addition to the lower or operating winding andthe upper or winding, the middle winding of relay H4, is permanently connected to the upper or tip conductor of the trunk. The other end of this winding is connected, by `means of rmultiple conductor |23 of cable |2| to Athe key-set of each master Vsubscribers station, suchas key-sets |02, andl |04,v at which point the conductor is either looped-or dead-ended depending upon whether the key-set is associated withv theflrst or an intermediate station or with the last stationA of the group. Conductor |23, therefore, closely parallels conductor |22; and, as indicated by the dotted capacities shown between the various conductors of cable |2|, bothof these conductors are equally exholding winding. One end of this compensating 1 posed to any inductive disturbance on any of the conductorsof the cable.` The middlev or compen- Satine .winding and ,the lower or.,operzatlxlaWind-1 ing of relay H4 have the same number of turns each and are of equal resistance. These two windings, however, are wound in opposite directions on the core of the relay. Any inductive disturbance on the multiple connections between the various stations of the group is, therefore, neutralized since it sets up opposing currents of equal intensity in both the lower and middle windings of relay H4. The balanced condition across trunk |00 is thus maintained thereby eliminating the possibility of cross-talk or other inductive disturbances from aiecting conversation over the trunk.

What is claimed is:

1. In an intercommunicating telephone system, a plurality of subscribers stations, a trunk line from a central oiice multipled at each of said stations, a telephone set at each station, means at each station for connecting the respective telephone set to the trunk line, a multi-winding relay associated with the trunk, switching means at one of said stations for connecting one winding of said relay in series with the telephone set across said trunk to cause operation of the relay, contact means associated with said relay and closed when the relay is operated to connect a second winding of said relay in a holding bridge, including a resistance, across said trunk to hold said relay operated when said switching means is released, a series relay in said trunk line adapted to be operated whenever any of said telephones are connected to the trunk, said relay being arranged, when operated, to short-circuit said second winding to cause the multi-wound relay to release and remove the holding bridge from the trunk.

2. In an intercommunicating telephone system, a plurality of subscribers stations, a trunk line from a central office multipled at each of said stations, a telephone set at each of said stations, means at each station for connecting the respective telephone to the trunk, a multiwinding relay associated with the trunk, switching means at one of said stations for connecting one winding of said relay in series with the telephone across said trunk to cause operation of the relay, contact means associated with said relay responsive to its operation to connect a second winding of said relay across said trunk to hold said relay operated when said switching means is released, a series relay in said trunk adapted to be operated when any of said telephones is connected to the trunk and when operated to cause said second Winding bridge across the trunk to be removed.

3. In an intercommunicating telephone system, a plurality of subscribers stations, a trunk line from a central office multipled at each of said stations, a telephone set at each of said stations, means at each station for connecting the respective telephone set to the trunk line, a multiwinding relay associated with the trunk, switching means at each station, a first winding 0n said relay having one terminal multipled to all of said switching means, any one of said switching means when operated being adapted to connect said first winding across the trunk in series with the telephone to operate the relay, a second winding on said relay having one terminal connected to a terminal of the first winding and having its other terminal extended to closely parallel the multiple connection of said rst winding to all of said switching means, said second winding being of the same resistance and having the same number of turns as the first winding, but so connected that any current owing in the rst winding caused by inductive disturbances ef.- fecting the multiple connection to the switching means will be neutralized in the relay due to an equal opposing current set up by the disturbance in the parallel extension of the second winding, contact means associated with said multi-wound relay and closed when the relay is operatedto connect a third winding thereof in a holding bridge across said trunk and hold said relay operated when said switching means is released, a series relay in said trunk circuit adapted to be operated whenever any of said telephones is connected to the trunk, said series relay being adapted when operated to cause said multi-wound relay to release and disconnect said holding bridge.

4. In an intercommunicating telephone system, a plurality of subscribers stations, a telephone set at each station, a cable connecting all stations, a trunk line from a central oice contained in said cable and multipled to each of said stations, a multi-winding relay associated with the trunk line, a rst winding on Said relay having one terminal connected to a conductor of said trunk line and the other terminal connected to a holding conductor in said cable which is multipled at each station, switching means at each station for connecting the respective telephone across the trunk line in series with said holding conductor and rst winding, a second winding on said relay of the same characteristics as the iirst winding and having one terminal connected in multiple with the rst winding terminal to the trunk line and the other terminal connected to another conductor of. said cable, said second winding being Connected diierentially with respect to the rst Winding whereby cross-talk currents ilo-wing in said holding conductor and rst winding will be neutralized in the relaxT by similar currents flowing in the other cable conductor and second winding.

WILLIAM M. BEAUMONT. 

